As many people are getting interested in a well-being life these days, the concern for one's health is also getting higher. However, as foodstuff such as meat, fish and shellfish which is likely to dacay in normal temperature, the foodstuff has been stored in frozen condition or been hurriedly transported within a short time after butchery.
However, when meat such as beaf, mutton having a larger portion of red muscular fibers is frozen, calcium ions are eluted from mitochondria of the red muscular fibers in the low temperature or low oxygen condition, and thus, the calcium coherence of sarcoplasmic reticulum therein becomes lower, and the calcium concentration near the myofibril becomes higher, and then, a cold shortening occurs to prompt the shrinkage of muscles, to break the nutrition thereof and to make the meat more tough.
More concretely, as time goes on after cattle, sheep or pigs are killed, glycogen of creatine phosphate in the muscle thereof begins to be consumed, the level of ATP is lowered into below some value, and irreversible actomyosin bridge between muscular fibers begins to be formed, thereby lowering the softness and extensibility. Accordingly, when creatine phosphate and glycogen is completely exhausted and when the pH value of the muscle reaches a maximum, the irreversible mutual combination between actin and myosin is prompted, and then, the muscle rigidity phenomenon of making the muscle tougher happens. That is, as meat undergoing the process of the muscle rigidity has reduced lengths of sarcomere, the lowered softness thereof and the lowered humidity therein, the meat should undergo an aging process.
Also, when temperature around the meat is sharply lowered after butchery or is highly maintained after butchery, the quality of the meat is badly influenced, thereby causing a problem that the meat requires longer ripening time.
FIG. 1 shows a shortening (i.e., shrinkage) degree of muscular fiber after butchery when meat is maintained at respective temperatures at which meat does not reach to the state of a muscle rigidity. That is, as shown in FIG. 1, the shortening degree of the muscular fiber becomes lowest near 18° C., and the shortening degree of the muscular fiber is fine in the range between 10° C. and 25° C. Thus, when the temperature becomes out of the range therebetween, as the shortening degree becomes higher, the meat becomes tough for people to eat. Especially, the shortening degree reaches high value of 50% when the temperature reaches 0° C. In this regard, the phenomenon is referred to as cold shortening that the pre-rigor muscle sharply becomes cold in the range between 0° C. and 16° C. This phenomenon is easily found in meat or mutton having higher portion of red muscle fiber. That is, in low temperature and oxygenless condition, as calcium ions are eluted from mitochondria, and as calcium coherence of sarcoplasmic reticulum therein becomes lower, the calcium concentration near the myofibril becomes higher thereby prompting the shortening of a muscle.
To the contrary, the shortening degree of muscular fiber is higher in high temperature condition above 18° C., which is referred to as heat shortening. The heat shortening is generated by that, enzymes related with ATPase and metabolic operation in muscles become activated by heat supply, and therefore, that ATP, CP, glycogen are resolved with higher speed, thereby prompting the rigidity after butchery.
Also, the muscle rigidity phenomenon is found in fish and shellfish as well as meat. That is, in order to store foodstuff such as meat, fish, shellfish, vegetables, fruits, if the foodstuff keeps freezed or refrigerated below 10° C., it is impossible to maintain the its freshness and also impossible to maintain its nutrition and flavor. Therefore, it has been highly required to freshly store foodstuff with maintaining its nutrition and flavor.